In Harry Potter's world, changing one's appearance is as simple as taking a few sips of Polyjuice Potion. But in real life, faking that magic on film is not so easy. For a sequence early in Harry Potter and the Deathly Hallows: Part One, six characters must morph into doppelgangers of Harry (Daniel Radcliffe) in order to confuse the evil wizard Voldemort (Ralph Fiennes) and his Death Eaters. To pull off the sequence, visual effects artists had to create digital hybrids that combined the facial characteristics of the original actors and Radcliffe. "We needed to have a little bit of the attributes of Harry, and a little bit of the attributes of whoever we started with—George, Fred, Ron, Hermione," says Nicolas Aithadi, VFX supervisor at Moving Picture Company, which created the scene's effects. "The tricky part is you have to be able to read the Harry part and the George part. What we keep from each of these characters has to be perfect."

Animators needed an immense amount of data on each actor's face to create the scene. To get it, they used the Mova Contour Reality Capture system, which first required the application of UV paint to the actors' faces. While invisible to the naked eye, the paint was picked up by Mova's rig of 29 cameras, which captured each actor's performance in real time. "The system allows you to capture up to 50,000 points of information about what the face is doing," says VFX supervisor Tim Burke. This includes skin, muscle and vein movement. The triangulation of the cameras allowed animators to create a 3D mesh cloud that they used as a basis for the characters. "Bodies we can do," Aithadi says. "Faces are quite difficult. Mova gave us the highest resolution facial movements we could find."

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Next came the tricky task of actually creating the hybrids. Head animator Dan Zelcs created tools that would allow VFX artists to reshape one face to another and blend portions of the face realistically and quickly. "We don't just transform linearly from one to the other," Aithadi says. "The ears can go over here, the nose can go over here. The jaw can shrink or grow." But it couldn't all be automated; there was quite a bit of fine-tuning done by hand, particularly to the eyelashes and eyebrows. "Mova gives us a lot of really fine facial details, but there are certain areas close to the eyes that it doesn't," Zelcs says. "We had to fill in the gaps there with our own sets of eye-rigging."

Once the CG models were tweaked to perfection, VFX artists replaced the actors' heads with the digi-doubles, which, although they're fully CG, truly show the actors' performances thanks to Mova's groundbreaking system. "It's a full CG, close-up character being driven by a live action performance," Burke says. The resulting hybrids, he says, are "these weird, weird looking people. Even having 75 percent Harry with Hermione's hair, it's pretty freaky."

But the sequence wouldn't be complete without seeing all seven Potters interacting with each other. Here, Director David Yates went old-school: He had the actors play their characters after the transformation; Radcliffe studied those performances, then mimicked them against a green screen, and the composite performances were stitched together into one shot just as they would have been twenty years ago. "There's him playing Hermione and him playing Ron, with little gags of what those characters would do," Burke says. "It's hilarious—a fun little sequence before we get into the more serious stuff." That would be the business of trying to defeat the seemingly all-powerful—and possibly immortal—Voldemort. But fans will have to wait until the second film, out July 2011, to see that epic battle.

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